<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>粒子特效</title>

<style>
html,body{
	margin:0px;
	width:100%;
	height:100%;
	overflow:hidden;
  background:#000;
}

#canvas{
	position:absolute;
	width:100%;
	height:100%;
}
</style>

</head>
<body>

<canvas id="canvas"></canvas>

<script>
function project3D(x,y,z,vars){

	var p,d;
	x-=vars.camX;
	y-=vars.camY-8;
	z-=vars.camZ;
	p=Math.atan2(x,z);
	d=Math.sqrt(x*x+z*z);
	x=Math.sin(p-vars.yaw)*d;
	z=Math.cos(p-vars.yaw)*d;
	p=Math.atan2(y,z);
	d=Math.sqrt(y*y+z*z);
	y=Math.sin(p-vars.pitch)*d;
	z=Math.cos(p-vars.pitch)*d;
	var rx1=-1000;
	var ry1=1;
	var rx2=1000;
	var ry2=1;
	var rx3=0;
	var ry3=0;
	var rx4=x;
	var ry4=z;
	var uc=(ry4-ry3)*(rx2-rx1)-(rx4-rx3)*(ry2-ry1);
	var ua=((rx4-rx3)*(ry1-ry3)-(ry4-ry3)*(rx1-rx3))/uc;
	var ub=((rx2-rx1)*(ry1-ry3)-(ry2-ry1)*(rx1-rx3))/uc;
	if(!z)z=0.000000001;
	if(ua>0&&ua<1&&ub>0&&ub<1){
		return {
			x:vars.cx+(rx1+ua*(rx2-rx1))*vars.scale,
			y:vars.cy+y/z*vars.scale,
			d:(x*x+y*y+z*z)
		};
	}else{
		return { d:-1 };
	}
}


function elevation(x,y,z){

	var dist = Math.sqrt(x*x+y*y+z*z);
	if(dist && z/dist>=-1 && z/dist <=1) return Math.acos(z / dist);
	return 0.00000001;
}


function rgb(col){

	col += 0.000001;
	var r = parseInt((0.5+Math.sin(col)*0.5)*16);
	var g = parseInt((0.5+Math.cos(col)*0.5)*16);
	var b = parseInt((0.5-Math.sin(col)*0.5)*16);
	return "#"+r.toString(16)+g.toString(16)+b.toString(16);
}


function interpolateColors(RGB1,RGB2,degree){

	var w2=degree;
	var w1=1-w2;
	return [w1*RGB1[0]+w2*RGB2[0],w1*RGB1[1]+w2*RGB2[1],w1*RGB1[2]+w2*RGB2[2]];
}


function rgbArray(col){

	col += 0.000001;
	var r = parseInt((0.5+Math.sin(col)*0.5)*256);
	var g = parseInt((0.5+Math.cos(col)*0.5)*256);
	var b = parseInt((0.5-Math.sin(col)*0.5)*256);
	return [r, g, b];
}


function colorString(arr){

	var r = parseInt(arr[0]);
	var g = parseInt(arr[1]);
	var b = parseInt(arr[2]);
	return "#"+("0" + r.toString(16) ).slice (-2)+("0" + g.toString(16) ).slice (-2)+("0" + b.toString(16) ).slice (-2);
}


function process(vars){


	if(vars.points.length<vars.initParticles) for(var i=0;i<5;++i) spawnParticle(vars);
	var p,d,t;

	p = Math.atan2(vars.camX, vars.camZ);
	d = Math.sqrt(vars.camX * vars.camX + vars.camZ * vars.camZ);
	d -= Math.sin(vars.frameNo / 80) / 25;
	t = Math.cos(vars.frameNo / 300) / 165;
	vars.camX = Math.sin(p + t) * d;
	vars.camZ = Math.cos(p + t) * d;
	vars.camY = -Math.sin(vars.frameNo / 220) * 15;
	vars.yaw = Math.PI + p + t;
	vars.pitch = elevation(vars.camX, vars.camZ, vars.camY) - Math.PI / 2;

	var t;
	for(var i=0;i<vars.points.length;++i){

		x=vars.points[i].x;
		y=vars.points[i].y;
		z=vars.points[i].z;
		d=Math.sqrt(x*x+z*z)/1.0075;
		t=.1/(1+d*d/5);
		p=Math.atan2(x,z)+t;
		vars.points[i].x=Math.sin(p)*d;
		vars.points[i].z=Math.cos(p)*d;
		vars.points[i].y+=vars.points[i].vy*t*((Math.sqrt(vars.distributionRadius)-d)*2);
		if(vars.points[i].y>vars.vortexHeight/2 || d<.25){
			vars.points.splice(i,1);
			spawnParticle(vars);
		}
	}
}

function drawFloor(vars){

	var x,y,z,d,point,a;
	for (var i = -25; i <= 25; i += 1) {
		for (var j = -25; j <= 25; j += 1) {
			x = i*2;
			z = j*2;
			y = vars.floor;
			d = Math.sqrt(x * x + z * z);
			point = project3D(x, y-d*d/85, z, vars);
			if (point.d != -1) {
				size = 1 + 15000 / (1 + point.d);
				a = 0.15 - Math.pow(d / 50, 4) * 0.15;
				if (a > 0) {
					vars.ctx.fillStyle = colorString(interpolateColors(rgbArray(d/26-vars.frameNo/40),[0,128,32],.5+Math.sin(d/6-vars.frameNo/8)/2));
					vars.ctx.globalAlpha = a;
					vars.ctx.fillRect(point.x-size/2,point.y-size/2,size,size);
				}
			}
		}
	}
	vars.ctx.fillStyle = "#82f";
	for (var i = -25; i <= 25; i += 1) {
		for (var j = -25; j <= 25; j += 1) {
			x = i*2;
			z = j*2;
			y = -vars.floor;
			d = Math.sqrt(x * x + z * z);
			point = project3D(x, y+d*d/85, z, vars);
			if (point.d != -1) {
				size = 1 + 15000 / (1 + point.d);
				a = 0.15 - Math.pow(d / 50, 4) * 0.15;
				if (a > 0) {
					vars.ctx.fillStyle = colorString(interpolateColors(rgbArray(-d/26-vars.frameNo/40),[32,0,128],.5+Math.sin(-d/6-vars.frameNo/8)/2));
					vars.ctx.globalAlpha = a;
					vars.ctx.fillRect(point.x-size/2,point.y-size/2,size,size);
				}
			}
		}
	}
}

function sortFunction(a,b){
	return b.dist-a.dist;
}

function draw(vars){

	vars.ctx.globalAlpha=.15;
	vars.ctx.fillStyle="#000";
	vars.ctx.fillRect(0, 0, canvas.width, canvas.height);

	drawFloor(vars);

	var point,x,y,z,a;
	for(var i=0;i<vars.points.length;++i){
		x=vars.points[i].x;
		y=vars.points[i].y;
		z=vars.points[i].z;
		point=project3D(x,y,z,vars);
		if(point.d != -1){
			vars.points[i].dist=point.d;
			size=1+vars.points[i].radius/(1+point.d);
			d=Math.abs(vars.points[i].y);
			a = .8 - Math.pow(d / (vars.vortexHeight/2), 1000) * .8;
			vars.ctx.globalAlpha=a>=0&&a<=1?a:0;
			vars.ctx.fillStyle=rgb(vars.points[i].color);
			if(point.x>-1&&point.x<vars.canvas.width&&point.y>-1&&point.y<vars.canvas.height)vars.ctx.fillRect(point.x-size/2,point.y-size/2,size,size);
		}
	}
	vars.points.sort(sortFunction);
}


function spawnParticle(vars){

	var p,ls;
	pt={};
	p=Math.PI*2*Math.random();
	ls=Math.sqrt(Math.random()*vars.distributionRadius);
	pt.x=Math.sin(p)*ls;
	pt.y=-vars.vortexHeight/2;
	pt.vy=vars.initV/20+Math.random()*vars.initV;
	pt.z=Math.cos(p)*ls;
	pt.radius=200+800*Math.random();
	pt.color=pt.radius/1000+vars.frameNo/250;
	vars.points.push(pt);
}

function frame(vars) {

	if(vars === undefined){
		var vars={};
		vars.canvas = document.querySelector("canvas");
		vars.ctx = vars.canvas.getContext("2d");
		vars.canvas.width = document.body.clientWidth;
		vars.canvas.height = document.body.clientHeight;
		window.addEventListener("resize", function(){
			vars.canvas.width = document.body.clientWidth;
			vars.canvas.height = document.body.clientHeight;
			vars.cx=vars.canvas.width/2;
			vars.cy=vars.canvas.height/2;
		}, true);
		vars.frameNo=0;

		vars.camX = 0;
		vars.camY = 0;
		vars.camZ = -14;
		vars.pitch = elevation(vars.camX, vars.camZ, vars.camY) - Math.PI / 2;
		vars.yaw = 0;
		vars.cx=vars.canvas.width/2;
		vars.cy=vars.canvas.height/2;
		vars.bounding=10;
		vars.scale=500;
		vars.floor=26.5;

		vars.points=[];
		vars.initParticles=700;
		vars.initV=.01;
		vars.distributionRadius=800;
		vars.vortexHeight=25;
	}

	vars.frameNo++;
	requestAnimationFrame(function() {
		frame(vars);
	});

	process(vars);
	draw(vars);
}
frame();
</script>
</body>
</html>

